Generally, X-rays decrease according to an X-ray attenuation coefficient of a target that is placed within X-ray beam paths, and the coefficient may be varied by a photoelectric effect, Compton scattering, etc.
An X-ray radiography device is a radiograph imaging device that obtains a two-dimensional (2D) projection image or a three-dimensional (3D) computed tomography image by using a characteristic of X-rays that penetrates a target, and the device includes an X-ray generator that emits X-rays and an X-ray detector that detects X-rays.
The X-ray generator includes a vacuum tube in which cathodes and anodes are provided and sealed. X-rays are generated by colliding heat electrodes that are emitted from cathodes by high power with a target of anodes. Herein, the X-rays generated from the X-ray generator are emitted in a sine wave according to an angle of the target. Thus, conventional X-ray generators include a collimator that controls an irradiation shape of the X-rays to a proper size such as cone beam size or fan beam size according to the size of the target or a radiograph purpose.
The X-ray detector includes a plurality of X-ray detecting elements arranged in a two dimensional matrix on a planar surface. Each of the X-ray detecting elements generates an electric signal that is proportional to an amount of incident X-rays on the X-ray detecting elements. Herein, conventional X-ray detectors include a signal processing circuit that generates projection data of the target by using electrical signals and positional information of each X-ray detecting element.
FIG.1 is a view showing an X-ray radiography device using a cone beam X-ray that is mainly used in dental clinics.
Referring to FIG. 1, the X-ray radiography device generally includes an X-ray generator 1 and an X-ray detector 2 that face each other with a target 3 interposed between the X-ray generator 1 and the X-ray detector 2.
X-rays generated from the X-ray generator 1 diffuse in a cone beam shape, transmit through the target 3 and are incident on the X-ray detector 2. X-ray detecting elements of the X-ray detector 2 generate electrical signals that are proportional to an amount of incident X-rays on the X-ray detecting elements. Therefore, the X-ray detector 2 may obtain an interior 2D projection image 4 of the target 3 by image processing projection data that are obtained by the electrical signals and positional information of the X-ray detecting elements. Further, a 3D computed tomography image of the target 3 may be obtained by reconstructing multi-directional projection data that are obtained by rotating the X-ray generator 1 and the X-ray detector 2.
Meanwhile, in a conventional X-ray radiography device, X-rays generated from the X-ray generator 1 diffuse in a cone shaped beam or a fan shaped beam, thus, a source to detector distance (SDD) between the X-ray generator 1 and the X-ray detector 2 may be secured to radiograph a target 3 having more than a predetermined size. In addition, the X-ray detector 2 having a wider or larger surface than the target 3 is required.
Accordingly, it is problematic in that size and manufacturing cost of an X-ray radiography device are increased. Further, image distortion such as geometric penumbra occurs within a radiograph.